"We consider this morning's earthquake to be an aftershock of the 2011 Northeastern Pacific Earthquake," said Yohei Hasegawa, an official at the Japanese meteorological agency.

The temblor, which struck just after 6 a.m. local time (5 p.m. ET Tuesday), was sparked by the Pacific tectonic plate "subducting," or moving under, the main land plate, he added.

Hasegawa warned that more tremors may be on the way.

"It's not just limited to this area alone, but the Northeastern Pacific Earthquake was an extremely powerful tremor, and its aftershocks are still continuing," he said.

The magnitude-9.0 earthquake on March 11, 2011, caused a devastating tsunami and killed more than 18,000 people.

Wednesday's quake didn't trigger a tsunami warning or cause any injuries or damage, although the bullet train that runs from Sendai City to Shin-Aomori was suspended for two hours while the train operator conducted a safety inspection.